The Leveson inquiry into the culture, practice and ethics of the press has summoned a political blogger to give evidence after a document purporting to be the evidence of Tony Blair's former communications adviser, Alastair Campbell, was released on a blog three days before it was due to be heard.

Lord Justice Leveson called on Paul Staines to appear before the inquiry to investigate how a version of Campbell's evidence – which included his fear that a newspaper may have hacked his phone messages, and into those of the then prime minister's wife Cherie Blair while she was living at No 10 – came to appear on the Order-Order website, which he runs under the pseudonym Guido Fawkes.

A statement on the inquiry website said the judge was very concerned to hear of the publication in spite of strict confidentiality agreements under which witness statements are disclosed in order that witnesses may prepare for the evidence.

"The website asserts that this statement was obtained by 'legal means' but Lord Justice Leveson will be enquiring further into this claim and Mr Paul Staines will be required to give evidence pursuant to section 21 of the Inquiries Act 2005," it said. "Witness statements are disclosed under strict confidentiality agreements in order that participants can prepare for the evidence; that confidentiality must be observed to maintain the integrity of the inquiry."

Campbell said on Twitter he was "genuinely shocked someone has seen fit to leak my statement to Leveson". Staines' website published extracts from what it claimed to be Campbell's evidence and a link to a document.

It is understood that the evidence published may be an early draft which differs from what Campbell finally submitted to the inquiry.

The inquiry said: "In the interests of fairness to Mr Campbell and others, Lord Justice Leveson has directed (and Mr Campbell has agreed) that his statement, which had been amended slightly, should be published on Monday on the inquiry website."

Campbell was due to give evidence on Wednesday morning and has prepared a wide-ranging critique of the media, sections of which were extracted on the Guido Fawkes blog.

The controversy comes at the start of the third week of hearings. Last week was dominated by the testimonies of Kate and Gerry McCann, the parents of Madeleine McCann, and Margaret Watson, from Glasgow, who told the inquiry how her son killed himself after reading derogatory articles about his dead sister. Actors Steve Coogan and Hugh Grant also took the stand along with JK Rowling and Sienna Miller.

Appearingon Monday will be Chris Jefferies, the Bristol landlord who won libel damages from eight national newspapers after they ran inaccurate and defamatory stories about him following the murder of his tenant Joanna Yates in December 2010. The singer Charlotte Church will be questioned about alleged phone hacking of her family and the former TV presenter Anne Diamond will also speak. Diamond was involved in an acrimonious divorce from Mike Hollingsworth and their private lives were written about extensively by the tabloid press.

, Nick Davies, the Guardian journalist who has led the phone-hacking revelations, will be questioned ahead of former tabloid reporters, Richard Peppiatt and Paul McMullan.

Peppiatt has confessed to making up stories while he was at the Daily Star. He has said he was ordered to do so and was paid a £150 bonus when he did.

Paul McMullan is a former deputy features editor at the News of the World who has publicly defended phone hacking and criticised Steve Coogan for "bleating" about it in a memorable clash on Newsnight.